There are five subtypes of muscarinic receptors that serve various important physiological functions in the central nervous system and the periphery. Mental functions like attention, learning, and memory are attributed to the muscarinic M1 subtype. These functions decline during natural aging and an early deficit is typical for Alzheimer s disease. In addition, stimulation of the M1 receptor increases non-amyloidogenic processing of the amyloid precursor protein and thus prevents accumulation of noxious beta-amyloid fragments. The selectivity of classical muscarinic agonists among receptor subtypes is very low due to the highly conserved nature of the orthosteric binding site among receptor subtypes. Herein we summarize some recent studies with the functionally-selective M1 agonist xanomeline that indicate complex pharmacological profile of this drug that includes interactions with and activation of receptor from both orthosteric and ectopic binding sites, and the time-dependent changes of ligand binding and receptor activation. These findings point to potential profitability of exploitation of ectopic ligands in the search for truly selective muscarinic receptor agonists.

Department of Neurochemistry Institute of Physiology Academy of Sciences of the Czech Republic Prague Czech Republic

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Novel long-acting antagonists of muscarinic ACh receptors

Long-term activation upon brief exposure to xanomleline is unique to M1 and M4 subtypes of muscarinic acetylcholine receptors